1. Field of the Invention
The present invention relates generally to an optical apparatus, and more particularly to a RGB beam combiner.
2. Description of the Related Art
As shown in FIG. 1, a conventional RGB beam combiner 3, which is equipped in a projector to combine color light beams L1˜L3 into one beam L4, includes a first prism 51 and a second prism 52, a third prism 53, and a fourth prism 54 coupled together. Between the first and the second prisms 51, 52 and between the third and the fourth prisms 53, 54 respectively are provided with a film to allow the first the second color light beams L1, L2 to transmit through, and reflect the third color light beam L3. Between the second the third prisms 52, 53 and between the first and the fourth prisms 51, 54 respectively are provided with a film to allow the second and the third color light beams L2, L3 to transmit through, and reflect the first color light beam L1.
Therefore, when the first color light beam L1 enters the beam combiner 3 via the first prism 51, the fourth prism 54, and the third prism 53 respectively, finally, they L1, L2, L3 will be combined to form a composite light beam L4 and come out via the second prism 52.
With advancement in technology, more and more people use projectors in seminar, video conference, or just simply watch movie. The projectors have to be made smaller and lighter for portability. The conventional beam combiner 3 is constructed by four prisms 51˜54, and the color light beams L1˜L3 enters the beam combiner 3 in three different directions that the projector must leave a large space for the prisms 51˜54 and for the beams L1˜L3 transmission. It can't be equipped in a small projector.
To overcome the aforesaid drawback, an improved beam combiner 4, taught in U.S. patent 20070091449, includes a first beam splitter 61, a second beam splitter 62 and a third beam splitter 63, wherein the third beam splitter 63 is parallelogram between the first and the second beam splitters 61 and 62. Between the first and the third beam splitters 61 and 63 is provided with a film to allow the second color light beam L2 to transmit through and reflect the first color light beam L1, and between the third and second beam splitters 63 and 62 is provided with a film to allow the first and the second color light beams L1, L2 to transmit through and reflect the third color light beam L3.
Therefore, the color light beams L1˜L3 may be combined in the second beam splitter 62 to form the composite light beam L4. The size of the beam combiner 4 is smaller and the first and the third color light beams L1, L3 enter the beam combiner 3 in the same direction that the beam combiner 3 needs a smaller space in the projector. However, it still has its limitations and that needs to be improved.